Definitely interesting work. I had not seen mention of citrofortunella hybrids like Indio Mandarinquat, the rind is amazing and if you let them hang long enough they are sweet. I think the smaller leaves also helps them when there is less water.
I found it interesting that mandarins, pomelos, and citrons are all zygotic, since all commercial citrus traces back to these three "parents".
Microcitrus are very interesting too, especially since they have resistance to citrus greening. Apparently Microcitrus spp. can cross with Citrus ichangensis, see the link below.
The hybrids of the two should be really interesting and cold hardy.